The present inventive concept herein relates to optical communication systems, and more particularly, to a multi-channel optical module that can transmit or receive an optical signal having a plurality of wavelengths using one optical fiber. In case of an active optical cable (AOC) such as a high definition multimedia interface (HDMI), a displayPort, a digital visual interface (DVI), etc. of which demand is increasing recently, 4 or more channels is required which can focus 4 or more wavelengths on one optical fiber to transmit A/V data. However, most of AOC on the market have a structure using 4 or 2 optical fibers. A cable having that structure has a disadvantage that installation and maintenance thereof are difficult and this makes a long distance transmission of optical signal difficult.
A conventional multi-channel optical module that can focus a plurality of wavelengths on one optical fiber has a structure that a beam is reflected in zigzag form using a coarse wavelength division multiplexing (CWDM) filter to be optically coupled. In this case, since an optical path difference between wavelengths is great, a general focusing lens cannot be used and an alignment is very difficult.
In case of multi-channel optical module having a structure that a plurality of optical transmission parts or optical reception parts based on TO-CAN processing one wavelength is aligned with a metal housing, and then the plurality of optical transmission parts or optical reception parts are fixed by a laser welder, an optical coupling is not easy. This is because the multi-channel optical module has a structure that the optical signal is reflected or penetrated by an optical filter mounted in the metal housing to optically couple to one optical fiber.
The multi-channel optical module comprises two sides of 45° on which filters are mounted. Since the two sides of 45° have V-groove shape, the processing of the sides is very difficult. In particular, it is almost impossible to polish a side of 45° and processability of side of 45° is very bad. The multi-channel optical module has a structure that it is processed in a cylindrical form and rotates in a metal housing and thereby an optical path is tilted. Thus, in the case that a mismatching occurs due to the rotation, efficiency of optical coupling to an optical fiber is low.
In case of a multi-channel optical module using a conventional WDM optical filter, since a distance between wavelengths of light source used for wavelength division is great, arrival times of wavelengths are different from one another when transmitting wavelengths a long distance and thereby a long distance transmission is difficult. Therefore, a delay time correction circuit is needed.
In case of an optical module of 4 or more channels, since it is difficult to produce the optical module in a single body, two or more filters are used. In this case, since a filter and a holder are separately mounted, locations of the filter and the holder are different from each other and thereby the filter cannot be aligned with the holder. An incident beam or an output beam is tilted. The more the number of channels is, the more serious those phenomenon is.